In digital circuits the nature of the output circuit is determined by the nature of the load element. Where the load element can be or is returned to a source of operating power the driver circuit may simply be the open collector of a switched transistor. However where the load element does not include a return to a source of power the driver circuit must include an active output terminal pull up device. Such a configuration involving both a transistor current sink pull down and an active pull up device is commonly referred to as a totem pole circuit. In general a totem pole output circuit has a low output impedance in the logic high state which optimizes transmission speed and device fan out. Open collector output is necessary where more than one device is used to send information over a common bus at the same time.
IEEE standard 488-1978 relates to a GENERAL PURPOSE INTERFACE BUS (GPIB) It describes a high speed system and requires that the driver output stage be pin selectable for either open collector or totem pole operation. The invention relates to devices suitable for integrated circuit (IC) drivers that meet the recommended standards.